1. Field of the Invention
This invention relates to highly conductive electrolyte composites and a method of fabricating highly conductive electrolyte composites and more particularly to fabricating electrolyte composites by combining ionically conductive compounds with ionically conductive soda glasses.
2. Background of the Invention
Research of Na/S and Na/MCl.sub.2 (M=Fe or Ni) cells continues in the search for advanced battery designs with improved power density and performance. Both battery types require high surface-area electrolytes for maximum performance.
Crystalline, ionically conductive compounds, such as the beta-aluminas, are the usual electrolytes for the advanced designs. The beta-aluminas are hexagonal structures with the approximate composition AM.sub.11 O.sub.17. The mobile ion A is a monovalent ion, such as Na, K, Rb, Ag, Tl or Li, and M is a trivalent ion, such as Al, Fe, or Ga. Related structures, i.e., .beta.'-alumina and B"-alumina occur with the approximate formulas AM.sub.7 O.sub.8 and AM.sub.5 O.sub.8, respectively. .beta."-alumina has extremely high conductivities; on the order of 1.4.times.10.sup.-1 (ohm-cm).sup.-1 at 250.degree. C., for sodium ions.
While the ionically conductive compounds, such as the beta-aluminas, have excellent sodium conductivities, their high sintering temperatures, on the order of 1400.degree. C., makes them difficult and expensive to fabricate into electrolyte structures for batteries. Therefore, the typical techniques of using ionically conductive compounds solely as the constituent for electrolytes is not economically feasible, due to their high-temperature, closed system handling requirements.
To overcome the electrolyte fabrication problems associated with crystalline, ionically conductive compounds, a variety of ionically conductive glasses have been developed, such as those disclosed by U.S. Pat. Nos. 4,544,614 and 4,465,744. These electrolytes exclude crystalline and undissolved constituents, such as the beta-aluminas, from their structures. Despite the exclusion of crystalline material, such as the beta-aluminas, from the general formulas of the ionically conductive glasses disclosed in the above mentioned patents, these glasses exhibit high soda characteristics. As such, the disclosure of U.S. Pat. Nos. 4,544,614 and 4,465,744 are incorporated herein by reference for the high soda glass constituent of the invention.
While U.S. Pat. Nos. 4,544,614 and 4,465,744 are effective for their intended purposes, a need exists for an electrolyte possessing an ionic conductivity closer to that of the beta-aluminas while also possessing the ease of fabrication of glass.
Ideally, an electrolyte composite comprised of an ionically conductive glass and an ionically conductive compound would take advantage of the properties of both materials to provide an economical and low resistance alternative to typical electrolyte structures.